1. Field of the Invention
This invention relates to method for the treatment of a semiconductor wafer and more particularly to a method for the treatment of a semiconductor wafer by the impartation of a mechanical distortion to the surface of the semiconductor wafer, which method represses defilement of the treatment surface of the semiconductor wafer with impurities and permits effective removal of impurities adhering to the treated surface in consequence of the impact employed for the mechanical distortion.
2. Description of the Prior Art
In recent years, the trend of semiconductor devices toward further size reduction and further addition to the scale of integration of components on a chip has come to impose increasingly exacting demands on semiconductor wafers which are destined to form substrates of semiconductor devices. One of these demands consists in repressing the occurrence of a crystal defect in the substrates formed of semiconductor wafers in the process of manufacture of semiconductor devices.
As a technique for attaining this repression of crystal defect, the gettering method which comprises forming a distortion field outside the area for device formation in the process of fabrication of the device and causing heavy metals and other impurities being unintentionally introduced into this area to be collected in the distortion field has been known to the art. This gettering method comes under two major versions, intrinsic gettering (IG) and extrinsic gettering (EG).
The intrinsic gettering method has been proposed by Tan et al. of IBM. It is based on the principle of forming a defectless layer on the surface of a wafer and a layer of high defect concentration inside the wafer. Specifically, the method comprises subjecting the supersaturating oxygen being introduced into a Czochralski (CZ) crystal pulled up by the CZ technique to a heat treatment at a temperature in the neighborhood of 1,000.degree. C. thereby inducing precipitation of the oxygen in the form of an oxide like cristobalite and utilizing this precipitate as a source layer for the generation of defects in a high concentration. This method is subdivided into three types by the combination of heat treatments performed at low temperatures in the range of from 650.degree. C. to 800.degree. C. and at high temperatures exceeding 1,000.degree. C. Unlike the extrinsic gettering, the intrinsic gettering entails the difficulty in necessitating accurate control of oxygen concentrations and ensuring uniform distribution thereof in the bulk crystals not withstanding the advantage that the impurities to be introduced from the external sources are small in volume and that the effect of treatment is maintained until completion of the process.
The extrinsic gettering falls under a mechanical method and a physicochemical method. The mechanical method consists in inflicting a mechanical damage upon the rear surface of a wafer and heat-treating the wafer sustaining the damage thereby inducing a dislocation. The physicochemical method is further divided under two types, one resorting to diffusion of phosphorus and the other effecting the gettering by the implantation of ion in the rear surface of a wafer.
As the mechanical method, the practice of impinging quartz particles or alumina particles on the rear surface of a semiconductor wafer has been adopted heretofore. The lattice distortion which is consequently introduced into the rear surface of the semiconductor wafer is called a "backside damage," the extent of which constitutes itself an important factor for the gettering technique mentioned above.
The conventional method for the formation of such a backside damage as described above has entailed the problem that the impinged quartz particles or alumina particles are broken into smaller fragments and these fragments are suffered to persist as foreign matter on or in the semiconductor wafer under treatment and form a cause for rendering semiconductor devices such as LSI rejectable on account of defective quality in the process of fabrication. Moreover, the fragments of quartz or alumina contain in high concentration impurities different from the material of the semiconductor substrate and, therefore, form a cause for pollution of semiconductor devices in the process of fabrication, induce the occurrence of lattice defects in the semiconductor wafers, and rather degrade the yield of production than ensure the manifestation of the gettering effect and improve the yield of production.
For the solution of this problem, the method which comprises impinging ice particles against the rear surface of a semiconductor wafer has been proposed. By this method, however, the density of lattice defects to be introduced cannot be freely varied and controlled as desired because the ice particles have a fixed specific gravity and have their individual weights automatically determined by their own diameters and they have a fixed hardness. Particularly since the ice has a small specific gravity of 0.917 g/cm.sup.3, the magnitude of dynamic energy which can be imparted to the ice particles has its own limit and, as a result, the extent of the damage which can be inflicted by the ice particles on the semiconductor wafer has its own limit.